1 /*
   2  * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "precompiled.hpp"
  26 #include "classfile/javaClasses.hpp"
  27 #include "classfile/stringTable.hpp"
  28 #include "classfile/systemDictionary.hpp"
  29 #include "classfile/vmSymbols.hpp"
  30 #include "code/codeCache.hpp"
  31 #include "code/icBuffer.hpp"
  32 #include "gc_implementation/shared/gcHeapSummary.hpp"
  33 #include "gc_implementation/shared/gcTimer.hpp"
  34 #include "gc_implementation/shared/gcTrace.hpp"
  35 #include "gc_implementation/shared/gcTraceTime.hpp"
  36 #include "gc_interface/collectedHeap.inline.hpp"
  37 #include "memory/genCollectedHeap.hpp"
  38 #include "memory/genMarkSweep.hpp"
  39 #include "memory/genOopClosures.inline.hpp"
  40 #include "memory/generation.inline.hpp"
  41 #include "memory/modRefBarrierSet.hpp"
  42 #include "memory/referencePolicy.hpp"
  43 #include "memory/space.hpp"
  44 #include "oops/instanceRefKlass.hpp"
  45 #include "oops/oop.inline.hpp"
  46 #include "prims/jvmtiExport.hpp"
  47 #include "runtime/fprofiler.hpp"
  48 #include "runtime/handles.inline.hpp"
  49 #include "runtime/synchronizer.hpp"
  50 #include "runtime/thread.inline.hpp"
  51 #include "runtime/vmThread.hpp"
  52 #include "utilities/copy.hpp"
  53 #include "utilities/events.hpp"
  54 
  55 void GenMarkSweep::invoke_at_safepoint(int level, ReferenceProcessor* rp, bool clear_all_softrefs) {
  56   guarantee(level == 1, "We always collect both old and young.");
  57   assert(SafepointSynchronize::is_at_safepoint(), "must be at a safepoint");
  58 
  59   GenCollectedHeap* gch = GenCollectedHeap::heap();
  60 #ifdef ASSERT
  61   if (gch->collector_policy()->should_clear_all_soft_refs()) {
  62     assert(clear_all_softrefs, "Policy should have been checked earlier");
  63   }
  64 #endif
  65 
  66   // hook up weak ref data so it can be used during Mark-Sweep
  67   assert(ref_processor() == NULL, "no stomping");
  68   assert(rp != NULL, "should be non-NULL");
  69   _ref_processor = rp;
  70   rp->setup_policy(clear_all_softrefs);
  71 
  72   GCTraceTime t1(GCCauseString("Full GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, _gc_tracer->gc_id());
  73 
  74   gch->trace_heap_before_gc(_gc_tracer);
  75 
  76   // When collecting the permanent generation Method*s may be moving,
  77   // so we either have to flush all bcp data or convert it into bci.
  78   CodeCache::gc_prologue();
  79 
  80   // Increment the invocation count
  81   _total_invocations++;
  82 
  83   // Capture heap size before collection for printing.
  84   size_t gch_prev_used = gch->used();
  85 
  86   // Capture used regions for each generation that will be
  87   // subject to collection, so that card table adjustments can
  88   // be made intelligently (see clear / invalidate further below).
  89   gch->save_used_regions(level);
  90 
  91   allocate_stacks();
  92 
  93   mark_sweep_phase1(level, clear_all_softrefs);
  94 
  95   mark_sweep_phase2();
  96 
  97   // Don't add any more derived pointers during phase3
  98   COMPILER2_PRESENT(assert(DerivedPointerTable::is_active(), "Sanity"));
  99   COMPILER2_PRESENT(DerivedPointerTable::set_active(false));
 100 
 101   mark_sweep_phase3(level);
 102 
 103   mark_sweep_phase4();
 104 
 105   restore_marks();
 106 
 107   // Set saved marks for allocation profiler (and other things? -- dld)
 108   // (Should this be in general part?)
 109   gch->save_marks();
 110 
 111   deallocate_stacks();
 112 
 113   // If compaction completely evacuated all generations younger than this
 114   // one, then we can clear the card table.  Otherwise, we must invalidate
 115   // it (consider all cards dirty).  In the future, we might consider doing
 116   // compaction within generations only, and doing card-table sliding.
 117   bool all_empty = true;
 118   if (level == 1) {
 119     all_empty = gch->young_gen()->used() == 0;
 120   }
 121 
 122   GenRemSet* rs = gch->rem_set();
 123   assert(level == 1, "Code will break if this isn't true.");
 124   Generation* old_gen = gch->old_gen();
 125   // Clear/invalidate below make use of the "prev_used_regions" saved earlier.
 126   if (all_empty) {
 127     // We've evacuated all generations below us.
 128     rs->clear_into_younger(old_gen);
 129   } else {
 130     // Invalidate the cards corresponding to the currently used
 131     // region and clear those corresponding to the evacuated region.
 132     rs->invalidate_or_clear(old_gen);
 133   }
 134 
 135   CodeCache::gc_epilogue();
 136   JvmtiExport::gc_epilogue();
 137 
 138   if (PrintGC && !PrintGCDetails) {
 139     gch->print_heap_change(gch_prev_used);
 140   }
 141 
 142   // refs processing: clean slate
 143   _ref_processor = NULL;
 144 
 145   // Update heap occupancy information which is used as
 146   // input to soft ref clearing policy at the next gc.
 147   Universe::update_heap_info_at_gc();
 148 
 149   // Update time of last gc for all generations we collected
 150   // (which currently is all the generations in the heap).
 151   // We need to use a monotonically non-decreasing time in ms
 152   // or we will see time-warp warnings and os::javaTimeMillis()
 153   // does not guarantee monotonicity.
 154   jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
 155   gch->update_time_of_last_gc(now);
 156 
 157   gch->trace_heap_after_gc(_gc_tracer);
 158 }
 159 
 160 void GenMarkSweep::allocate_stacks() {
 161   GenCollectedHeap* gch = GenCollectedHeap::heap();
 162   // Scratch request on behalf of oldest generation; will do no
 163   // allocation.
 164   ScratchBlock* scratch = gch->gather_scratch(gch->old_gen(), 0);
 165 
 166   // $$$ To cut a corner, we'll only use the first scratch block, and then
 167   // revert to malloc.
 168   if (scratch != NULL) {
 169     _preserved_count_max =
 170       scratch->num_words * HeapWordSize / sizeof(PreservedMark);
 171   } else {
 172     _preserved_count_max = 0;
 173   }
 174 
 175   _preserved_marks = (PreservedMark*)scratch;
 176   _preserved_count = 0;
 177 }
 178 
 179 
 180 void GenMarkSweep::deallocate_stacks() {
 181   if (!UseG1GC) {
 182     GenCollectedHeap* gch = GenCollectedHeap::heap();
 183     gch->release_scratch();
 184   }
 185 
 186   _preserved_mark_stack.clear(true);
 187   _preserved_oop_stack.clear(true);
 188   _marking_stack.clear();
 189   _objarray_stack.clear(true);
 190 }
 191 
 192 void GenMarkSweep::mark_sweep_phase1(int level,
 193                                   bool clear_all_softrefs) {
 194   // Recursively traverse all live objects and mark them
 195   GCTraceTime tm("phase 1", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
 196   trace(" 1");
 197 
 198   GenCollectedHeap* gch = GenCollectedHeap::heap();
 199 
 200   // Because follow_root_closure is created statically, cannot
 201   // use OopsInGenClosure constructor which takes a generation,
 202   // as the Universe has not been created when the static constructors
 203   // are run.
 204   assert(level == 1, "We don't use mark-sweep on young generations");
 205   follow_root_closure.set_orig_generation(gch->old_gen());
 206 
 207   // Need new claim bits before marking starts.
 208   ClassLoaderDataGraph::clear_claimed_marks();
 209 
 210   gch->gen_process_roots(level,
 211                          false, // Younger gens are not roots.
 212                          true,  // activate StrongRootsScope
 213                          SharedHeap::SO_None,
 214                          GenCollectedHeap::StrongRootsOnly,
 215                          &follow_root_closure,
 216                          &follow_root_closure,
 217                          &follow_cld_closure);
 218 
 219   // Process reference objects found during marking
 220   {
 221     ref_processor()->setup_policy(clear_all_softrefs);
 222     const ReferenceProcessorStats& stats =
 223       ref_processor()->process_discovered_references(
 224         &is_alive, &keep_alive, &follow_stack_closure, NULL, _gc_timer, _gc_tracer->gc_id());
 225     gc_tracer()->report_gc_reference_stats(stats);
 226   }
 227 
 228   // This is the point where the entire marking should have completed.
 229   assert(_marking_stack.is_empty(), "Marking should have completed");
 230 
 231   // Unload classes and purge the SystemDictionary.
 232   bool purged_class = SystemDictionary::do_unloading(&is_alive);
 233 
 234   // Unload nmethods.
 235   CodeCache::do_unloading(&is_alive, purged_class);
 236 
 237   // Prune dead klasses from subklass/sibling/implementor lists.
 238   Klass::clean_weak_klass_links(&is_alive);
 239 
 240   // Delete entries for dead interned strings.
 241   StringTable::unlink(&is_alive);
 242 
 243   // Clean up unreferenced symbols in symbol table.
 244   SymbolTable::unlink();
 245 
 246   gc_tracer()->report_object_count_after_gc(&is_alive);
 247 }
 248 
 249 
 250 void GenMarkSweep::mark_sweep_phase2() {
 251   // Now all live objects are marked, compute the new object addresses.
 252 
 253   // It is imperative that we traverse perm_gen LAST. If dead space is
 254   // allowed a range of dead object may get overwritten by a dead int
 255   // array. If perm_gen is not traversed last a Klass* may get
 256   // overwritten. This is fine since it is dead, but if the class has dead
 257   // instances we have to skip them, and in order to find their size we
 258   // need the Klass*!
 259   //
 260   // It is not required that we traverse spaces in the same order in
 261   // phase2, phase3 and phase4, but the ValidateMarkSweep live oops
 262   // tracking expects us to do so. See comment under phase4.
 263 
 264   GenCollectedHeap* gch = GenCollectedHeap::heap();
 265 
 266   GCTraceTime tm("phase 2", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
 267   trace("2");
 268 
 269   gch->prepare_for_compaction();
 270 }
 271 
 272 class GenAdjustPointersClosure: public GenCollectedHeap::GenClosure {
 273 public:
 274   void do_generation(Generation* gen) {
 275     gen->adjust_pointers();
 276   }
 277 };
 278 
 279 void GenMarkSweep::mark_sweep_phase3(int level) {
 280   GenCollectedHeap* gch = GenCollectedHeap::heap();
 281 
 282   // Adjust the pointers to reflect the new locations
 283   GCTraceTime tm("phase 3", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
 284   trace("3");
 285 
 286   // Need new claim bits for the pointer adjustment tracing.
 287   ClassLoaderDataGraph::clear_claimed_marks();
 288 
 289   // Because the closure below is created statically, we cannot
 290   // use OopsInGenClosure constructor which takes a generation,
 291   // as the Universe has not been created when the static constructors
 292   // are run.
 293   assert(level == 1, "We don't use mark-sweep on young generations.");
 294   adjust_pointer_closure.set_orig_generation(gch->old_gen());
 295 
 296   gch->gen_process_roots(level,
 297                          false, // Younger gens are not roots.
 298                          true,  // activate StrongRootsScope
 299                          SharedHeap::SO_AllCodeCache,
 300                          GenCollectedHeap::StrongAndWeakRoots,
 301                          &adjust_pointer_closure,
 302                          &adjust_pointer_closure,
 303                          &adjust_cld_closure);
 304 
 305   gch->gen_process_weak_roots(&adjust_pointer_closure);
 306 
 307   adjust_marks();
 308   GenAdjustPointersClosure blk;
 309   gch->generation_iterate(&blk, true);
 310 }
 311 
 312 class GenCompactClosure: public GenCollectedHeap::GenClosure {
 313 public:
 314   void do_generation(Generation* gen) {
 315     gen->compact();
 316   }
 317 };
 318 
 319 void GenMarkSweep::mark_sweep_phase4() {
 320   // All pointers are now adjusted, move objects accordingly
 321 
 322   // It is imperative that we traverse perm_gen first in phase4. All
 323   // classes must be allocated earlier than their instances, and traversing
 324   // perm_gen first makes sure that all Klass*s have moved to their new
 325   // location before any instance does a dispatch through it's klass!
 326 
 327   // The ValidateMarkSweep live oops tracking expects us to traverse spaces
 328   // in the same order in phase2, phase3 and phase4. We don't quite do that
 329   // here (perm_gen first rather than last), so we tell the validate code
 330   // to use a higher index (saved from phase2) when verifying perm_gen.
 331   GenCollectedHeap* gch = GenCollectedHeap::heap();
 332 
 333   GCTraceTime tm("phase 4", PrintGC && Verbose, true, _gc_timer, _gc_tracer->gc_id());
 334   trace("4");
 335 
 336   GenCompactClosure blk;
 337   gch->generation_iterate(&blk, true);
 338 }